Wooseok Choi

Market reaction to e-commerce impairments evidenced by website outages

Abstract This study examines the stock market reaction to announcements of website outages. Outages impair business to consumer electronic commerce, potentially resulting in significant losses to affected organizations. Anecdotal evidence suggests a negative impact of outages on the market value of the organization; however there has not been any formal empirical analysis. We find a significant negative correlation between website outage announcements and stock returns, and the correlation is increasing in the percentage of revenues earned through Internet business. We also report differential results dependent on the type of outage, but find no evidence of differential response associated with length or frequency of outages. Our findings would support significant expenditures to prevent future website outages.

Fabrication, characterization and application of a microelectromechanical system (MEMS) thermopile for non-dispersive infrared gas sensors

We report on the design, fabrication, and characterization of a non-dispersive infrared (NDIR) gas sensor using an integrated thermopile on a micromachined silicon nitride membrane. The NDIR sensor consists of an optical cavity with new specular reflectors around the light bulb. The multi-layer absorber showed an absorptance of over 90% at 3.3–4.9 µm. The thermopile with this absorber has an output voltage of 144.83 mV at a 5 mW incident power and a sensitivity of 30 V W−1. The sensitivity of the thermopile packaged with a Fresnel lens was 51 V W−1, approximately 1.7 times higher than that of a thermopile with only an absorber. This is due to the decrease in thermal mass and heat loss from a hot junction, and due to the increase in absorptance. Using this newly fabricated thermopile, we developed a small and sensitive NDIR gas detector module for accurate air quality monitoring systems for energy-saving buildings and automotive applications. Our novel sample cavity design is configured to uniformly emit collimated light into the entrance aperture of the cavity to enhance the sensitivity of the NDIR gas detector.

CEO's Operating Ability and the Association between Accruals and Future Cash Flows

This study investigates whether an individual CEOs operating ability, operationalized as the extent to which an individual CEO utilizes the companys assets efficiently to generate profits, explains the association between accruals and future cash flows. While this mapping can be driven by both the quality of accounting measurement and CEO operating ability, there is little empirical evidence on the latter link. After controlling for the CEOs accounting estimation ability, we find that the association between current period accruals and future cash flows is stronger when the CEO demonstrates superior operating ability. This suggests that a CEOs operating ability is an important determinant of the informativeness of current accruals for future cash flows.

A front-side dry-etched thermopile detector with 3–5 μm infrared absorber and its application to novel NDIR CO 2 gas sensors

We present a front-side micromachined thermopile with high sensitivity in the 3-5 mum window, and discuss its application to a novel non-dispersive infrared (NDIR) CO2 gas sensor with a light source emitting collimated light. The micromachined thermopile shows a measured sensitivity of 30 mV/W and a D* of 0.3 times 108 cmradicHz/W. Using this newly fabricated thermopile, we also have successfully developed a small, sensitive NDIR CO2 detector module for accurate air quality monitoring systems in energy-saving building and automotive applications. The novel sample cavity comprising specular reflectors around the light bulb is configured to uniformly emit collimated light into the entrance aperture of the cavity in order to enhance the sensitivity of NDIR CO2 detector.

The effect of different levels of internal control over financial reporting regulation on the quality of accounting information: evidence from Korea

This study investigates the effect of different levels of internal control over financial reporting (ICFR) regulations on accounting information quality. Stricter ICFR regulation restricts the opportunistic behavior of managers, leading to better accounting information quality. Strictly regulated firms tend to report lesser discretionary accruals. The results of this study indicate that the accounting information quality of less strictly regulated firms deteriorated, while there was no significant change in the accounting information quality of strictly regulated firms. This implies that the effect of ICFR regulation depends more on the enforcement rather than the adoption of the regulations.

Pre-Tax Income Forecasts and Tax Avoidance

When analysts issue both earnings and pre-tax income forecasts, they implicitly provide a forecast of income tax expense. We find that these pre-tax income forecasts have a negative (positive) effect on corporate tax avoidance for firms with relatively aggressive (non-aggressive) tax policy. We also find evidence that analysts providing implicit income tax expense forecasts have more accurate earnings forecasts and have a better appreciation of how tax expense affects future earnings. Overall, these results suggest that analysts’ implicit tax expense forecasts increase transparency and play an important role in deterring both overly aggressive and overly conservative corporate tax avoidance.

Design, fabrication, and characterization of piezoresisitve strain gage-based pressure sensors for mechatronic systems

The pressure sensor is a key device in many mechatronic systems for automotive and industrial applications. We represent the piezoresitive pressure sensor based on the single crystal silicon strain gauges, which are glass-fused to the stainless steel diaphragm at high temperature. The silicon bulkmicromachined strain gauges have the through holes and the closed structure, unlike the current competitive devices with open structure. This unique design concept reduces shifting or rotation of gauge position during glass frit bonding and enables the automation of alignment and bonding processes, which improves the sensor performance and yield and hence reduces sensor cost. The prototype was characterized using specific long term tests such as PPTCB (pulsed pressure, temperature cycling, with bias). The pressure sensors tested under pressure ranging from 0 to 50 bar at different temperature have a linear output with a typical sensitivity of about 16mV/V/bar and an offset drift of -6 mV to 2 mV. The fatigue life tests run at a rate of 3 Hz up to 2 million pressure cycles from 0 to 50 bar showed no failures when the pressure cycle test was stopped.